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The RETRACE-3D project (centRal italy EarThquakes integRAted Crustal model) focused on the revision of all the available geological and geophysical data in the area interested by the 2016-2018 seismic sequence of central Italy, with the final aim to reconstruct a reliable and consistent 3D geological model of that area. It is based on a collaboration, which was framed into a formal agreement, between Dipartimento della Protezione Civile (the Italian Civil Protection Department), Istituto di Geologia Ambientale e Geoingegneria, and Istituto per il Rilevamento Elettromagnetico of the Consiglio Nazionale delle Ricerche, Istituto Nazionale di Geofisica e Vulcanologia, and Istituto Superiore per la Protezione e la Ricerca Ambientale. The agreement purpose was to develop a project aimed at the geological and seismotectonic characterisation of the crustal volume hosting that seismic sequence. We present and discuss the approach, methodology and results of the project. The 3D geological model of the study area is developed in detail down to a depth of about 12 km, and extended to the Moho based on available regional-scale information. The model is available on the RETRACE-3D project website (www.retrace3d.it).

The NEAM Tsunami Hazard Model 2018 (NEAMTHM18) is a probabilistic hazard model for tsunamis generated by earthquakes. It covers the coastlines of the North-eastern Atlantic, the Mediterranean, and connected seas (NEAM). NEAMTHM18 was designed as a three-phase project. The first two phases were dedicated to the model development and hazard calculations, following a formalized decision-making process based on a multiple-expert protocol. The third phase was dedicated to documentation and dissemination. The hazard assessment workflow was structured in Steps and Levels. There are four Steps: Step-1) probabilistic earthquake model; Step-2) tsunami generation and modeling in deep water; Step-3) shoaling and inundation; Step-4) hazard aggregation and uncertainty quantification. Each Step includes a different number of Levels. Level-0 always describes the input data; the other Levels describe the intermediate results needed to proceed from one Step to another. Alternative datasets and models were considered in the implementation. The epistemic hazard uncertainty was quantified through an ensemble modeling technique accounting for alternative models’ weights and yielding a distribution of hazard curves represented by the mean and various percentiles. Hazard curves were calculated at 2,343 Points of Interest (POI) distributed at an average spacing of ∼20 km. Precalculated probability maps for five maximum inundation heights (MIH) and hazard intensity maps for five average return periods (ARP) were produced from hazard curves. In the entire NEAM Region, MIHs of several meters are rare but not impossible. Considering a 2% probability of exceedance in 50 years (ARP≈2,475 years), the POIs with MIH >5 m are fewer than 1% and are all in the Mediterranean on Libya, Egypt, Cyprus, and Greece coasts. In the North-East Atlantic, POIs with MIH >3 m are on the coasts of Mauritania and Gulf of Cadiz. Overall, 30% of the POIs have MIH >1 m. NEAMTHM18 results and documentation are available through the TSUMAPS-NEAM project website (http://www.tsumaps-neam.eu/), featuring an interactive web mapper. Although the NEAMTHM18 cannot substitute in-depth analyses at local scales, it represents the first action to start local and more detailed hazard and risk assessments and contributes to designing evacuation maps for tsunami early warning. © Copyright © 2021 Basili, Brizuela, Herrero, Iqbal, Lorito, Maesano, Murphy, Perfetti, Romano, Scala, Selva, Taroni, Tiberti, Thio, Tonini, Volpe, Glimsdal, Harbitz, Løvholt, Baptista, Carrilho, Matias, Omira, Babeyko, Hoechner, Gürbüz, Pekcan, Yalçıner, Canals, Lastras, Agalos, Papadopoulos, Triantafyllou, Benchekroun, Agrebi Jaouadi, Ben Abdallah, Bouallegue, Hamdi, Oueslati, Amato, Armigliato, Behrens, Davies, Di Bucci, Dolce, Geist, Gonzalez Vida, González, Macías Sánchez, Meletti, Ozer Sozdinler, Pagani, Parsons, Polet, Power, Sørensen and Zaytsev.

The SPOT Project (potentially triggerable offshore seismicity and tsunamis) is aimed at helping Italian authorities to comply with the application of the Safety of Offshore Oil and Gas Operations European Directive (2013/30/EU) and the ensuing Italian codes. An extensive reconstruction of offshore geological structures is being implemented in order to assess the existence of potentially seismogenic faults in the surroundings of offshore oil and gas platforms, as a propaedeutic step for the assessment of potentially triggered seismicity connected with operations on such platforms. The descriptive parameters of the identified faults will be used to estimate their natural earthquake rates. The impact of these natural earthquakes along the coasts will then be modeled in terms of expected ground shaking and tsunamis. In turn, these models will be used to estimate potential human and economic losses in a multi-hazard approach to risk assessment. Wherever the combined earthquake and tsunami modeling indicates a relevant impact along the coasts, a more detailed analysis will be carried out, also involving the operators of the related platforms, to perform specific models which also take into account production data. The project has been conceived and funded by the Italian Ministry of Economic Development, with the technical support of the National Department of Civil Protection. The involved research institutes are the Institute of Marine Sciences of the National Research Council (ISMAR), the National Institute of Geophysics and Volcanology (INGV), the European Centre for Training and Research in Earthquake Engineering (EUCENTRE), and the Laboratories University Network of Seismic Engineering (ReLUIS).

Young and tectonically active mountain chains like Central Apennines (Italy), characterized by a high structural complexity, represent astonishing examples for making strong inferences on seismotectonics. Repeated cycles of tectonic phases recognized by surface geology result in the development of a series of interacting fault systems as well as in a widespread reactivation of inherited structures, usually disarticulating pre-existing tectonic arrangements. In this context, what is observable at surface might mask a different structural architecture at depth, where shallow structures may be decoupled from the deeper ones. In the last decades, Central Apennines have been affected by a complex pattern of seismicity, which has been associated to the activation of both single faults and complex fault systems. Within the framework of the RETRACE-3D project, we reviewed a large set of underground data acquired for hydrocarbons explorations in the area struck by the 2016-2018 Central Apennines seismic sequence. Main goal is to build a comprehensive 3D geological model able to match the superficial observations with the deeper ones, and with the recent seismicity. Although the current extensional tectonic regime, results primarily show that the main architecture of this portion of the chain is still dominated by previous compressional large-scale structures, widespread evidence of segmentation, reactivation and even inversion of various sets of inherited faults. A reliable 3D geological modelling down to seismogenic depths as well as the recognition of reactivated paleo-structures play a fundamental role in understanding the seismotectonics of the considered area, also allowing to more robustly infer on the seismogenic potential of faults. This work would also open new points of discussion regarding information and input data needed to improve the assessment of seismic hazard in mountain chains such as the Central Apennines.

After the seismic events occurred in Emilia (Italy) on May 20th and May 29th, 2012, the International Commission on Hydrocarbon Exploration and Seismicity in the Emilia Region (ICHESE) evaluated the possible links between E&P activities and the seismic activity in the area affected by the earthquakes. The Commission could not rule out the possibility of a link and emphasized the need of further analyses, in order to exclude the correlation of seismic events of May 2012 to waste-water injection activities performed at the Cavone field. The Ministry of Economic Development (MiSE), the Emilia-Romagna Region and the Operator with the patronage of Assominerariai carried out such analyses and found new elements against the possibility that operations could affect the seismic events. Furthermore, the Commission recommended developing new integrated monitoring systems for seismicity, ground deformations and pore pressures that were able to provide high-quality data in real time, in order to support the analysis of the possible link between the human activities and the detected seismicity. In our presentation, we describe the lessons learned after the 2012 seismicity with reference to the initiatives undertaken by MiSE to improve and optimize knowledge and management of E&P sector in a seismically active territory as Italy is

We investigate a large geodetic data set of interferometric synthetic aperture radar (InSAR) and GPS measurements to determine the source parameters for the three main shocks of the 2016 Central Italy earthquake sequence on 24 August and 26 and 30 October (M-w 6.1, 5.9, and 6.5, respectively). Our preferred model is consistent with the activation of four main coseismic asperities belonging to the SW dipping normal fault system associated with the Mount Gorzano-Mount VettoreMount Bove alignment. Additional slip, equivalent to a Mw similar to 6.1-6.2 earthquake, on a secondary (1) NE dipping antithetic fault and/or (2) on a WNW dipping low-angle fault in the hanging wall of the main system is required to better reproduce the complex deformation pattern associated with the greatest seismic event (the Mw 6.5 earthquake). The recognition of ancillary faults involved in the sequence suggests a complex interaction in the activated crustal volume between the main normal faults and the secondary structures and a partitioning of strain release.

Understanding the relationship between seismogenic slip at depth and surface deformation is fundamental in any seismic hazard analysis because the assessment of the earthquake potential of large continental faults relies largely on field investigations. The well-documented 6 April 2009, Mw 6.3, L'Aquila earthquake affords a unique opportunity to explore the relationships between the activity of the deep source and its surface evidence. We used available high-resolution geologic, geodetic and seismological data aided by analogue modeling to reconstruct the geometry of the seismogenic rupture in relation with surface and sub-surface faults. We contend that the earthquake was caused by a blind fault, controlled at depth by pre-existing discontinuities and expressed at the surface by pseudo-primary breaks resulting from coseismic crustal bending. Finally, we propose a scheme for hierarchizing normal faults that explains all surface occurrences related to blind faulting in the frame of a single, mechanically coherent, interpretative model. Failure to appreciate such complexity may result in severe over– or under-estimation of the local seismogenic potential.

Over the past few years the assessment of the earthquake potential of large continental faults has increasingly relied on field investigations. State-of-the-art seismic hazard models are progressively complementing the information derived from earthquake catalogues with geological observations of active faulting. Using these observations, however, requires full understanding of the relationships between seismogenic slip at depth and surface deformation, such that the evidence indicating the presence of a large, potentially seismogenic fault can be singled out effectively and unambiguously. We used observations and models of the 6 April 2009, Mw 6.3, L'Aquila, normal faulting earthquake to explore the relationships between the activity of a large fault at seismogenic depth and its surface evidence. This very well-documented earthquake is representative of mid-size yet damaging earthquakes that are frequent around the Mediterranean Basin, and is somehow paradigmatic of the nature of the associated geologic evidence along with observational difficulties and ambiguities. Thanks to available high-resolution geologic, geodetic and seismological data aided by analogue modeling, we reconstructed the full geometry of the seismogenic source in relation with surface and sub-surface faults. We find that the earthquake was caused by seismogenic slip in the range 3-10 km depth, and that the slip distribution was strongly controlled by inherited discontinuities. We also contend that faulting was expressed at the surface by pseudo-primary breaks resulting from coseismic crustal bending and by sympathetic slip on secondary faults.Based on our results we propose a scheme for hierarchizing normal faults through which all surface occurrences related to faulting at depth can be interpreted in the frame of a single, mechanically coherent model. Appreciating such complexity is crucial to avoid severe over- or under-estimation of the local seismogenic potential.

The connection between fault-zone architecture and seismic behaviour is central to study the seismic potential of an active area. On November 23th, 1980, a Ms 6.9 earthquake struck the Irpinia area in Southern Italy. After the earthquake, several investigations produced divergent seismotectonic models based on different techniques, among others field geology observations, aftershock distribution, geodetic analysis, teleseismic observations, etc.. We re-analyzed all available data resulting from the aforementioned techniques with the aim to understand and reduce such divergence, and to achieve fuller understanding of the 1980 Irpinia sequence and to devise an accurate seismotectonic model. We used different data sets available in literature to create a tree-dimensional database using Midland Valley Software package (Move), and it is aimed in particular at integrating surface and subsurface data. The Database contains: 1) surface geological information extracted by available geological maps; 2) the seismicity from 1980 to 2011 (Italian Seismic Bulletin, INGV) and a detail on the local seismicity from 2007 to 2012 (Irpinia Seismic Network, ISNet bulletin of AMRA scarl); 3) all the seismic sections publicly available from the Videpi database and the crustal section Crop04, as well as deep well data; 4) seismogenic sources proposed by different authors. The combination of these data allowed us to constrain the orientation of the normal fault system responsible of the 1980 Irpinia events. We confirm that three different fault segments are the causative faults of the three main events recorded during the sequence, though we propose a new orientation of these structures. To test our model, we explore how these sub-events interact, cluster, propagate, and inhibit each other, through Coulomb static stress change analysis. We then show how our model capture much of the observed features of the seismicity of the area: both about the 1980 sequence and to recent (2007- 2012) background seismicity well recorded by local seismic network (ISNet). We conclude that the cross-correlation between geological and seismological data allow to model in detail seismogenic structures, and to achieve fuller understanding of seismic sequence in complex geological areas.

The deep structures of the Central–Southern Apennines are analysed on the basis of the regional component of gravity anomalies, obtained applying a stripping technique. This procedure allows the accurate removal of the gravimetric effect of the three-dimensional shallow (within the first 10 km) geological bodies from the observed Bouguer anomaly. The resulting anomaly map differs quite significantly from the Bouguer anomaly map, providing new constraints on the nature of the deeper part of the crust and on the upper mantle. The stripping reveals that the regional gravity lows are shifted westward in comparison with Bouguer anomaly lows. Moreover, the gravimetric pattern indicates a lack of cylindrism for the deep structures of the Apennine Chain, which in the study area can be roughly divided into three main segments. The observed differences between the gravity anomalies pattern of the Central Apennines and that of the Southern Apennines are marked.The integration of gravimetric results with other geophysical data suggests that: (i) a ramp-dominated style for the buried Apulia (Adria) units and part of the underlying basement is compatible with gravimetric data and (ii) most of the regional gravity anomalies in the Central Apennines seem to originate within the lower crust.

The aim of this paper is to define the structural geometry and kinematics of Neogene deformation of the Matese Massif in order to validate the applicability of either thin-skinned or thick-skinned compressive styles in the Apennines. The Matese structure appears as a single N-vergent thrust sheet above a low angle thrust fault, which was later deformed by footwall thrust sheets. The massif is com-posed mainly of Mesozoic carbonates of inner platform to by-pass and slope facies, separated within the thrust sheet by high angle faults with small component of re-verse displacements. These faults acted as normal faults in the Mesozoic and Ceno-zoic and affected the carbonate facies distribution. During Neogene compression they were mildly reactivated and then passively truncated by the basal short-cut thrust fault that cut from pre-Triassic units to Jurassic dolostone towards the foreland. Finally, Quaternary extensional tectonics dissected the thrust sheet displacing it by up to 1000 m. This has resulted in the present-day structural setting of the Matese Massif as a horst bounded to the SW and NE by extensional basins filled with continental deposits.

In the Apennine fold and thrust belt of Italy, «thin-skinned» (i.e. detachment-dominated) and «thick-skinned» (i.e. crustal ramp-dominated) structures coexist, but with marked differences in both time and space. The external part of the northern Apennines and the deeper and younger portions (buried Apulian carbonates) of the thrust belt in the central and southern Apennines show limited amounts of shortening (in the range of 5–14 km). These result from similar deformation styles, involving the occurrence of relatively low-displacement, thick-skinned thrust ramps. The latter represent, at least in the northern Apennines, preexisting basement structures reactivated and inverted during contractional deformation. Interposed between the northern and southern parts of the fold and thrust belt, the central Apennines appear to constitute a transitional area in which strike-slip tectonics is relevant and carbonate platform units become predominant over pelagic basin ones, whereas the overall structure of the thrust belt becomes similar to that of the southern Apennines. In the latter, a peculiar structural style is revealed by the integrated analysis of surface and subsurface data. Structurally, the upper part of the thrust belt consists of allochthonous units made of Mesozoic peritidal carbonate platform and pelagic basin successions, and of Miocene foredeep sediments. These are completely detached from their original substratum and transported onto the 6–7 km thick, foreland carbonates of the Apulian platform. Based on available seismic data, the latter appears to be involved, together with the underlying Permo-Triassic clastics and, we infer, also the basement, in relatively low-displacement, thick-skinned structures. Therefore, in the southern Apennines, a transition from thin-to thick-skinned tectonics appears to have occurred through time. Thin-skinned structures characterise the shallower — and older — part of the thrust belt made of detached units, while a thick-skinned tectonic style is dominant in the buried Apulian carbonates of most recent accretion. The present boundary between the two different, superposed portions of the thrust belt consists of a low-angle, large-displacement thrust fault penetrated by numerous oil wells. Different styles and modes of contractional deformation in the investigated sectors of the Apennines appear to result from the geometrical requirement of maintaining strain compatibility and overall displacement continuity along a highly segmented orogen characterised by variable mechanical stratigraphy and southward increasing amounts of shortening.